Vaporizor body

ABSTRACT

A vaporizer body ( 1 ) having a vaporizing surface ( 3 ) for vaporizing metal in a PVD-metallization installation, wherein the vaporizing surface ( 3 ) comprises a plurality of recesses ( 5, 5′, 5 ″), with an opening of the respective recess having an area/perimeter-ratio of greater than or equal to 1.5 mm.

The present invention relates to a vaporizer body.

A common method for coating flexible substrates with metals is theso-called vacuum band metallization according to the PVD (physical vapordeposition) technology. Suitable flexible substrates are for examplepaper, plastic foils and textiles, and aluminum is mostly used as metal.Such coated substrates are widely used for wrapping and decorationpurposes, for the production of capacitors and in environmentaltechnology (insulation).

The coating of the flexible substrates takes place in so calledmetallization installations. In the metallization installation, thesubstrate to be coated is directed/guided over a cooled roll andmeanwhile exposed to a metal vapor which condensates on the surface ofthe substrate as a thin metal layer. For generating the required vaporflow of metal, resistance-heatable vaporizer bodies are used, e.g. inthe form of so called vaporizer boats, which are heated to approximately1450-1600° C. using a direct current flow. A metal wire is supplied tothe vaporizing surface (usually this is the upper side of the vaporizerbody), is liquefied on the vaporizing surface, and is vaporized undervacuum at approximately 10⁻⁴ mbar.

According to the PVD technology non-flexible substrates are coated batchwise in a discontinuous process, for example by means of flashvaporization. Non-flexible substrates are for example TV-screens andplastic parts.

For example, conventional vaporizer bodies consist of a hot-pressedceramic material, the main components of which are titanium diboride andboron nitride and/or aluminum nitride. In this connection, titaniumdiboride is the electrically conductive component, and boron nitrideand/or aluminum nitride are the electrically insulating component. Whenmixed together, these components result in specific electricalhot-resistances of 600-6000 μOhm*cm, wherein a mixing ratio ofconducting component to non-conducting component is respectively 50 mass% (+/−10 mass %).

In practice, a frequently occurring problem is the wetting of thevaporizing surface of the vaporizer body with/by the metal to bevaporized, in particular the initial wetting at the beginning of themetallization process. As a result, merely reduced vaporization rates(kilogram metal/time unit) can be realized at the beginning of themetallization process due to a smaller/reduced wetting surface. Further,when the vaporizing surface is wetted non-uniformly and incompletely,the problem exists that the conductibility of the vaporizer body, whichin total is electrically conductive, changes due to the metal to bevaporized being in contact with the vaporizer body (parallelresistance). Namely, the conductibility changes irregularly depending onthe amount and extension of supplied and vaporized metal. Accordingly,it is necessary to re-adjust the supply of current to the vaporizer bodyin order to be able to maintain a uniform vaporizing rate.

Therefore, in prior art a layer structure is often applied to thesurface of the vaporizer body forming the vaporizing surface in order toimprove the wettability with the metal to be vaporized.

Further, two-part vaporizer boats are known, having an electricallyconducting vaporizer body core part and an electrically insulatingvaporizer body outer part which receives/encases the core part, whereinthe outer part of the vaporizer body is made of a wetting promotingmaterial.

Further, from EP 1 688 514 A1 a ceramic vaporizer boat is known, thevaporizing surface of which is provided with a plurality ofgrooves/channels. The grooves are arranged such that they are notparallel to the direction of current flow, that is, the grooves areinclined with regard to the longitudinal axis of the vaporizer boat. Thegrooves have a width of 0.1 to 1.5 mm, a depth of 0.03 to 1 mm, and alength of at least 1 mm. The grooves are supposed to improve wettingwith liquid aluminum during vaporization operation. In particular,according to EP 1 688 514 A1, the grooves shall suppress/reduce awetting of the vaporizing surface in a longitudinal direction of thevaporizer body and shall promote a wetting of the vaporizing surface ina cross-direction of the vaporizer body, that is, by means of thegrooves a wider/broadened wetting of the vaporizer surface shall beobtained. This is mainly achieved by the following two effects. On theone hand, a kind of capillary action is achieved by the small width ofthe grooves, so that liquid aluminum in the grooves is “pulled” towardsthe longitudinal ends of the grooves. On the other hand, the temperaturewithin the grooves increases due to the reflection of heat radiation atthe side walls of the grooves. An increased temperature reduces thewetting angle so that wetting with the metal is improved.

Such a prior art vaporizer body is shown in FIG. 7, wherein the groovesare formed as transverse channels.

These known vaporizer boats have the disadvantage of a complexproduction since a great number of relatively thin grooves have to beprovided on the vaporizing surface. A further disadvantage is the factthat in a longitudinal direction of the vaporizer boat a uniform metalbath or metal melt is only formed, if the metal wire is supplied to acentral position in the longitudinal direction. This is because,starting from the contacting point of the metal wire, the metal bathextends towards both sides with an equal longitudinal extension. Asshown in FIG. 7, the vaporizing surface of the vaporizer boat will beincompletely wetted by the metal (in particular in the longitudinaldirection), if the contacting point of the metal wire is not arranged inthe center. Such a unilateral wetting has the effect that the metal bathflows onto the water-cooled copper fixation at one of the longitudinalsides, wherein the opposite side remains unwetted. Now, the oppositeside overheats since a cooling effect by the liquid metal melt ismissing.

From DE 20 2005 020 544 U1 a vaporizer device is known containing acrucible having a melting zone and a vaporizing zone which is inconnection with the melting zone.

DE 10 2005 057 220 A1 discloses a receptacle for vaporizing metal,wherein a plurality of grooves is formed on the bottom of the vaporizingsurface.

It is an object of the present invention to provide a relativelyinsensitive vaporizer body which is easy to operate and which allows anappropriate (i.e. substantially uniform and complete) wetting of thevaporizing surface with metal in both longitudinal direction and crossdirection of the vaporizer body, irrespective of the contacting point ofthe metal wire or the location of metal supply. Further, the vaporizerbody shall be easy and cheap to manufacture.

To this end, the present invention provides a vaporizer body accordingto claim 1. Further embodiments of the vaporizer body according to thepresent invention are described in the dependent claims.

The vaporizer body according to the present invention comprises avaporizing surface from which metal supplied thereto may be vaporized.For example, metal, such as aluminum, in the form of a metal wire may besupplied to the vaporizing surface. Alternatively or additionally, metalwhich is already molten may be supplied to the vaporizing surface. Incase of a metal wire, the metal supplied to the vaporizing surface isfirst liquefied/molten on the hot vaporizing surface, and issubsequently vaporized.

According to the invention the vaporizing surface comprises a pluralityof recesses, for example two to five recesses. Each recess has anopening with an area/perimeter ratio of greater than or equal to 1.5 mm,e.g. greater than or equal to 2 mm, e.g. greater than or equal to 3 mm.If for example a recess having a circular opening is provided, theradius of the opening is at least 3 mm. If for example a recess isprovided having an opening with the shape of a circular ring, the widthof the ring of the opening is at least 3 mm. If for example a recesshaving a square opening is provided, the side length of the opening isat least 6 mm.

The recesses have a wetting promoting effect which is primarily based ona change of the wetting angle at the edge between a sidewall of therecess and an adjacent part of the vaporizing surface. At this edge theliquid metal is dammed and flows along the edge and around the opening,so that the molten metal initially wets the vaporizing surface primarilyalong the edge. The wetting of the recess by “overhanging” dammed metaltakes place substantially abrupt. The area/perimeter ratio of greaterthan or equal to 1.5 mm promotes a wetting of the vaporizing surface inboth a longitudinal direction and a transverse direction of thevaporizer body. Further, such recesses turned out to be able to achievea uniform and large-area wetting of the vaporizing surface even if themetal is not centrally supplied so that an overflow of the metal mold isprevented. That is, the liquid metal substantially wets the entirevaporizing surface even if the point where the metal wire contacts thevaporizing surface is not in a center of the vaporizer surface.Therefore, the vaporizer body is easy to use and insensitive underoperating conditions. Further, the recesses are easy to manufacture.

For example, a cavity may be formed on the vaporizing surface, theplurality of recesses being formed in/on the bottom surface of thecavity. The cavity forms a boundary for the molten metal and prevents alateral overflow of the molten metal.

For example, the recesses may have a depth of 0.05 to 1 mm. For example,the recesses have a depth of 0.15 to 0.4 mm.

For example, the sidewall of the respective recess or depression mayform an angle of 80 to 150° with the part of the vaporizing surfacewhich is adjacent to the recess. The change of the wetting angle for theliquid metal at the edge is then (180−80)°=100° to (180−150)°=30°. Forexample, the angle may be in the range of 90 to 135°, for example in therange of 90 to 120°. In this connection, for example, the angle may beselected so that accumulation of molten metal at the edge between thesidewall and the adjacent part of the vaporizing surface is promoted,that is, so that a flow of molten metal into the recess is impeded, sothat during operation of the vaporizer body the molten metal initiallyflows mainly along the edge which is formed by the sidewall and the partof the vaporizing surface which is adjacent thereto (in the followingupper edge of the recess) and around the recess.

For example, the sidewall of the respective recess may bepartially/sectionally curved or consistently curved. For example, thesidewall may be curved at least in a portion adjacent to the bottomsurface of the recess, that is, in a portion of the edge between thebottom surface and the sidewall of the recess. Thereby, occurrence ofhot-spots during operation of the vaporizer body may be prevented. Ifthe recesses are made by milling, a corresponding milling cutter with acorner radius may be used. For example, the curvature may have a radiusof 0.05 to 3 mm, for example a radius of 0.1 to 1 mm, for example 0.3 to0.5 mm.

For example, the recesses may all have the same shape. Alternatively,the recesses may have different shapes. For example, one or more/severalor all of the openings may be formed circular or in the shape of acircular ring. For example, one or more or all of the openings may havethe form of an ellipse or an elliptical ring. For example, one or moreor all of the openings may have the shape of an equilateralquadrilateral (for example a square) or of an equilateral quadrilateralring, wherein two corners are arranged on the longitudinal axis of thevaporizer body so that a rhombus is formed. For example, one or more orall of the openings may have the form of an isosceles triangle ortriangular ring, wherein the hypotenuse of the respectivetriangle/triangular ring is arranged perpendicular to the longitudinalaxis of the vaporizer body.

For example, the plurality of recesses may be arranged in series in thelongitudinal direction of the vaporizer body. In this connection, forexample, the individual recesses may be spaced apart from each other.For example, the distance between the individual recesses may be 1 to 80mm, for example 2 to 10 mm, for example 3 to 8 mm. The distance betweenthe individual recesses may vary or may be constant. The individualrecesses may be either separated/isolated from each other or may beconnected with each other via a connecting channel. However, theindividual recesses may also abut each other or partly overlap eachother, thereby forming a neck. The individual recesses may be arrangedsubstantially central in a transverse direction of the vaporizer body,that is, on the longitudinal axis/symmetry axis of the vaporizer body.However, the recesses may also be arranged so as to be offset to ordisplaced from the longitudinal axis/symmetry axis of the vaporizerbody. Further, several recesses may be arranged in series in transversedirection of the vaporizer body.

For example, the vaporizer body may be formed as an electricallyinsulating vaporizer body outer part having an inner hollow space forreceiving an electrically conducting resistance-heatable vaporizer bodycore part. In this case, the outer part is heated via the inserted corepart. Alternatively, the vaporizer body may be integrally formed as anelectrically conductive resistant-heatable vaporizer body. In both casesthe vaporizing surface of the vaporizer body may be additionallyprovided with a wetting promoting layer/coating. Such a coating may alsoserve as a protection against abrasion and corrosion.

For example, the recesses may be formed by milling. Accordingly, anexisting vaporizer body may be converted in an easy and cheap manner, tothereby form the vaporizer body according to the present invention. Ifthe vaporizer body is formed by sintering a green body, the recesses maybe formed during the forming of the green body, for example bycorrespondingly impressing the mass of the green body. Thereby, postprocessing of the vaporizer body with a milling cutter or similar toolscan be facilitated or totally omitted.

In the following the present invention is described with reference tothe drawings by means of exemplary embodiments. In the drawings:

FIG. 1 a shows a top view of a vaporizer body according to a firstembodiment of the present invention,

FIG. 1 b shows a schematic top view of the vaporizer body of FIG. 1 aduring operation of the vaporizer body,

FIG. 1 c shows a further top view of the vaporizer body of FIG. 1 a,

FIG. 1 d shows a schematic detailed view of the vaporizer body of FIG. 1a during operation of the vaporizer body,

FIG. 2 shows a top view of a vaporizer body according to a secondembodiment of the present invention,

FIG. 3 shows a top view of a vaporizer body according to a thirdembodiment of the present invention,

FIG. 4 shows top views of further vaporizer bodies according to thepresent invention,

FIG. 5 and FIG. 6 respectively show a detailed view of a recess of avaporizer body according to the present invention, and

FIG. 7 shows a vaporizer body according to prior art.

FIG. 1 a shows a top view of a vaporizer body according to a firstembodiment of the present invention. The vaporizer body 1 is formed soas to have the shape of a so-called vaporizer boat, and consists of ahot-pressed ceramic material which contains as main components titaniumdiboride and boron nitride, wherein titanium diboride is theelectrically conductive component, and wherein boron nitride is theelectrically insulating component. The mixing ratio of conductingcomponent to non-conducting component is 50% (+/−10%) each, resulting ina specific resistance of approximately 600 to 6000 μOhm*cm. Thevaporizer body 1 is formed as a plate body, with a length ofapproximately 120 mm, a width of approximately 35 mm and a height ofapproximately 10 mm. Four cylindrical recesses or depressions 5 areformed in the vaporizing surface 3 of the vaporizer body 1, thevaporizing surface being formed by the upper side of the plate. Forexample, the recesses may be formed with a corresponding milling cutter.That is, according to this embodiment, each recess 5 has a circularopening and a circular bottom surface. The recesses 5 are arranged inseries in the longitudinal direction of the vaporizer body and areseparated from each other. According to this embodiment, the distancebetween the individual recesses 5 is approximately 5 mm, and therespective depth is approximately 0.3 mm. The diameter of the circularopening and the circular bottom surface of each recess is approximately20 mm. This results in a respective area/perimeter ratio (=r/2 or d/4for circular openings) of 5 mm.

FIG. 1 b schematically shows the vaporizer body 1 of FIG. 1 a duringoperation. Metal wire/aluminum was decentrally supplied onto thevaporizing surface 3, namely at the second recess 5 from the right side,as shown by reference sign 7. Nevertheless, a metal bath 9 could begenerated which uniformly wetted/covered substantially the entirevaporizing surface 3 without overflowing. In a detailed examination itcould be identified that the liquid aluminum was distributed along therespective circumference/perimeter of the opening (=edge betweensidewall of the recess 5 and adjacent vaporizing surface 3) (see forexample right side of the second recess from the left side). The effectwhich is responsible for this is shown in FIGS. 1 c and 1 d. As shown inFIG. 1 d, the molten metal 9 initially accumulates/is dammed at theupper edge of the recess 5. This is due to a change of the wetting angleby 90° at the upper edge of the recess 5. Thereby, the molten metal 9initially wets the vaporizing surface 3 primarily along the upper edgeof the recess 5, as indicated by arrows 11 in FIG. 1 c. The circularshape of the recesses 5 contributes to a particularly beneficialdistribution of the molten aluminum 9 on the vaporizing surface 3.Finally, also the recesses 5 and their bottom surfaces are wetted by themolten metal 9, that is by dammed aluminum.

As indicated by the dashed line in FIG. 1 c, a cavity 13 may beoptionally formed on the vaporizing surface 3, the four recesses 5 beingformed in/on the bottom surface of the cavity 13. The sidewall of thecavity 13 forms a barrier for the molten metal, whereby overflowing ofthe molten metal 9 can be prevented.

FIG. 2 shows a top view of a vaporizer body according to a secondembodiment of the present invention. The vaporizer body 1 comprises avaporizing surface 3 with two recesses 5′. The recesses 5′ respectivelyhave an opening with the shape of a circular ring and a bottom surfacewith the shape of a circular ring. The dimensions of the vaporizer body1 correspond to those of the first embodiment. The outer diameter of therespective opening and bottom surface is 30 mm, the respective innerdiameter being 18 mm. This results in an area/perimeter ratio of 3 mm(=ring width/2). The recesses 5′ respectively have a depth of 0.3 mm.The distance between the recesses 5′ is 25 mm.

FIG. 3 shows a top view of a vaporizer body according to a thirdembodiment of the present invention. The vaporizing surface 3 of thevaporizer body 1 comprises four recesses 5″. The opening and the bottomsurface of the respective recess 5″ have the shape of a ring with theform of an isosceles triangle. The recesses 5″ are arranged such thatthe hypotenuse of each triangular ring is substantially perpendicular tothe longitudinal axis/symmetry axis of the vaporizer body 1. The twoinner recesses 5″, that is the recesses being arranged adjacent to thelongitudinal centre of the vaporizer body, are arranged such that thehypotenuse faces away from the longitudinal centre. The two outerrecesses 5″ are arranged such that the hypotenuse faces the longitudinalcentre. Two recesses 5″ respectively form the shape of a rhombus. Thedimensions of the vaporizer body 1 correspond to those of the firstembodiment. The hypotenuse has a length of 25 mm and a width of 4 mm.The length of the two other triangular sides may be adjusted accordingto requirements so that an appropriate distribution of the molten metal9 in the longitudinal direction and the transverse direction isachieved. In the embodiment shown, the surface of the triangularopenings is respectively 148 mm², the perimeter/circumference beingrespectively 82.1 mm. This results in an area/perimeter ratio of 1.8 mm.The recesses 5″ respectively have a depth of 0.3 mm. The distancebetween the two inner recesses 5″ is 25 mm, the respective distancebetween inner and outer recess being 5 mm.

In the embodiments shown the number of the recesses (and also thespecified size and the specified area/perimeter ratio) may be variedaccording to requirements. Further, different forms may be combined witheach other. For example, two inner triangular recesses may beexclusively provided, or two inner triangular recesses may be combinedwith two outer circular recesses.

FIG. 4 shows further embodiments of the vaporizer body according to thepresent invention, that is, for the form of the opening of the recess,wherein—except for the last four examples—only one recess is shown pervaporizer body for simplification. Of course, the different forms of therecesses shown in FIG. 4 may be combined with each other and with theforms described above. As can be seen from FIG. 4, e.g., the opening ofthe recess 5 may have an elliptical form or the form of an ellipticalring. For example, the main axis of the ellipse may be perpendicular tothe longitudinal axis of the vaporizer body. Alternatively, the mainaxis may be parallel to or inclined with regard to the longitudinal axisof the vaporizer body.

As shown in the three lower most examples of FIG. 4, for example, the atleast two recesses may be in connection with each other via a connectionchannel or may partially overlap. For determining the respectivearea/perimeter ratio the circumferential line of the respectiverecess/opening may be simply symmetrically continued in the overlappingportion. If the two openings overlap, they form a neck/constriction ordent between the two recesses/openings. Also differently shaped openingsmay overlap.

The geometrical form of the recesses 5 or the openings thereof is notlimited to the forms shown. In fact, also other forms/openings may beused which have an area/perimeter ratio of greater than or equal to 1.5mm and which enable an appropriate wetting of the vaporizer body ifsuitably arranged on the vaporizing surface 3 of the vaporizer body 1.

FIG. 5 shows the recess 5 of a vaporizer body 1 according to the presentinvention in detail. The sidewall of the recess 5 has a curvature 15.Thereby, the occurrence of hot-spots in the region of the recess 5 maybe prevented/reduced during operation of the vaporizer body.

FIG. 6 shows the recess 5 of a vaporizer body 1 according to the presentinvention in detail. The sidewall of the recess forms an angle ofapproximately 90° with the part of the vaporizing surface 3 which isadjacent to the recess 5, thereby promoting the accumulation/damming ofthe molten metal 9 at the upper edge of the recess 5 at the beginning ofthe operation of the vaporizer body.

1. An electrically conducting vaporizer body, being resistance-heatablefor vaporizing metal and having a vaporizing surface for vaporizingmetal in a PVD-metallization installation, wherein the vaporizingsurface comprises a plurality of recesses, with an opening of therespective recess having an area/perimeter-ratio of greater than orequal to 1.5 mm.
 2. The vaporizer body according to claim 1, wherein thevaporizing surface comprises a cavity, the plurality of recesses beingformed in a bottom surface of the cavity.
 3. The vaporizer bodyaccording to claim 1, wherein the recesses have a depth of 0.05 to 1 mm.4. The vaporizer body according to claim 1, wherein a sidewall of therespective recess forms an angle of 80 to 150° with a portion of thevaporizing surface which is adjacent to the recess.
 5. The vaporizerbody according to claim 1, wherein a sidewall of the respective recessis curved at least in a portion which is adjacent to a bottom surface ofthe recess.
 6. The vaporizer body according to claim 1, wherein one orseveral or all of the openings are circular or have the shape of acircular ring.
 7. The vaporizer body according to claim 1, wherein oneor several or all of the openings have the shape of an ellipse or anelliptical ring.
 8. The vaporizer body according to claim 1, wherein oneor several or all of the openings are formed as a quadrilateral havingequal sides or as a quadrilateral ring having equal sides, wherein twocorners are arranged on a longitudinal axis of the vaporizer body. 9.The vaporizer body according to claim 1, wherein one or several or allof the openings have the shape of an isosceles triangle or an isoscelestriangular ring, and wherein a respective hypotenuse is arrangedperpendicular to a longitudinal axis of the vaporizer body.
 10. Thevaporizer body according to claim 1, wherein the plurality of recessesis arranged in series in a longitudinal direction of the vaporizer body.11. (canceled)
 12. (canceled)